The present invention relates to the preparation of novel polyester-imides and their use in coating wires with outstanding physical properties.
In Schmidt U.S. Pat. No. 3,697,471, there is disclosed in Example 9 a polyester-imide prepared from ethylene glycol, glycerine and a diimide dicarboxylic acid prepared by reacting two moles of trimellitic anhydride with one mole of methylene dianiline. This diimide dicarboxylic acid is sometimes abbreviated hereinafter as DID. The polymers prepared in Schmidt have a triol to diol molar ratio of 0.676, a hydroxy to carboxy equivalent ratio of 1.41. The product has a 250.degree. C. heat shock without using prestretch of the wire and employing one hour of baking.
The commercial material made under the Schmidt patent known as Terebec FH contains substantial amounts of ester derived from terephthalic acid and a small amount of imide derived from DID. Terebec FH in inferior in properties to the commercial polyester-imide, ISOMID, made in accordance with Meyer U.S. Pat. No. 3,426,098. Thus, in regard to heat shock precent passing one-half hour at 200.degree. C. using 20 percent prestretch, the following results are noted.
______________________________________ Mandrel Size Terebec FH ISOMID ______________________________________ 1X 30 0 2X 50 80 3X 60 100 4X 90 100 ______________________________________
When ISOMID was tested at 260.degree. C., the results in the same Mandrel Sizes was 0-0-0-0.
It has previously been proposed to use polyesterimide resins as a top coat for electrical conductors coated with a polyester resin or other resin, e.g., Ishizuka U.S. Pat. No. 4,208,464, Keske U.S. Pat. No. 4,070,524, Czajka U.S. Pat. No. 3,944,706, Keske U.S. Pat. No. 4,012,555, and Keske U.S. Pat. No. 4,012,556. However, the products of these patents do not have sufficiently good heat shock properties. In fact, a number of these patents, e.g., the Keske and Czajka patents, are directed to self-bonding coatings for magnet wires. The self-bonding property is incompatible with good heat shock properties. Ishizuka prepares a water soluble polyester-imide having an acid value of 30-50, an OH/COOH equivalent ratio of 1:1 to 2:1 and requires a substantial amount of an aliphatic polycarboxylic acid.